Researchers from Hungary and the UK have developed a single-dose H5N1 influenza vaccine that induces a protective level of immunity against infection in healthy adult and elderly volunteers. The vaccine is the first single-dose regimen to be tested in elderly subjects and it fulfills all European Union and U.S. licensing criteria offering a promising influenza A virus vaccine candidate. They report their findings in the February 2008 issue of the Journal of Virology.

New cases of human H5N1 infection continue to emerge worldwide resulting in severe illness and high fatality rates. In the case of a pandemic, vaccination is likely to be the most effective approach toward minimizing illness and death. Already a variety of candidate vaccines are being tested, however, most require two-dose regimens to be effective.

In the study researchers developed a whole-virion, inactivated, adjuvanted H5N1 vaccine and tested its safety and efficacy in healthy adult and elderly volunteers. Subjects were randomly assigned to receive one or two doses of 3.5 μg of the vaccine or one dose of 6 or 12 μg of the vaccine. Safety and side effects were monitored following vaccination and blood samples were collected to determine immune response. Occasional injection site pain, fever and fatigue were the only reported side effects and while antibody responses were observed in all the subjects, single doses of 6 μg or more fulfilled the European Union and U.S. licensing criteria.

"We found that the present vaccine is safe and immunogenic in healthy adult and elderly subjects and requires low doses and, unlike any other H5N1 vaccines, only one injection to trigger immune responses which comply with licensing criteria," say the researchers.